Low-Temperature Heterolytic Adsorption of H2 on ZnO(10(1)over-bar0) Surface

The interaction of molecular hydrogen with a ZnO(10 (1) over bar0) surface at cryogenic conditions was investigated by in situ scanning tunneling microscopy (STM) experiments combined with density functional theory (DFT) calculations. The H-2 molecules were found splitting at an extremely low temperature similar to 20 K and growing into a novel one-dimensional chain structure along the [0001] direction, which extends as long as several hundred nanometers and possesses substantial thermal stability up to similar to 220 K. Both high-resolution STM images and DFT calculations reveal that the initial H-2 splitting occurs through a physisorbed precursor state followed by forming heterolytic bonds to the Zn and O ions belonging to two neighbored Zn-O pairs of the ZnO(10 (1) over bar0) surface. These findings have shed new light on the active roles of ZnO in various hydrogen-related techniques as well as in hydrogenation reactions.